Finite element analysis of transpedicular fixation options in the thoracolumbar junction with a burst fracture of the Th12 vertebra during trunk extension

Background. The therapeutic strategy for burst neurologically intact fractures of the thoracolumbar spine continues to cause disagreement among surgeons, remaining a relevant topic for discussion. At the same time, when treating injuries of the thoracolumbar junction, surgical methods are generally preferred due to the biomechanical characteristics of this region. The purpose was to study the stress-strain state of a lumbar spine model with a burst fracture of the Th12 vertebra under various transpedicular fixation options during trunk extension. Materials and methods. A finite element model of the human thoracolumbar spine with a burst fracture of the Th12 vertebra was developed, along with a transpedicular stabilization system. Four transpedicular fixation options were modeled using short and long screws passing through the anterior surface of the vertebral body, as well as models with and without cross-links. Results. It was found that for models with short screws without cross-links, long screws without cross-links, short screws with cross-links, and long screws with cross-links, the stress values in the body of the injured vertebra were 19.7, 29.3, 19.2, and 29.0 MPa, respectively. Regarding the metal-bone contact zones, peak loads were identified at the screw entry point into the L2 vertebral arch and amounted to 11.1, 23.3, 11.1, and 22.1 MPa for the respective models. At the same time, the highest stress values were observed in the transpedicular screws within the L2 vertebral body — 42.9, 45.5, 40.6, and 42.8 MPa, respectively. Conclusions. During trunk extension, the use of cross-links reduces the stress levels at all control points of the models, regardless of the length of the fixation screws. However, the use of bicortical screws is associated with an increase in stress levels specifically in the injured vertebra.